SpiDME meeting, Nijmegen, May 2007 Stefano Sanvito and Nadjib Baadji Computational Spintronics Group School of Physics and CRANN, Trinity College

People Dr. Nadjib Baadji (Uni. Strasbourg), April ‘07 Mr. Sankar Kesanakurthi (U. Hiderabad), April ‘07 Visits Sanvito to Hamburg (Feb. 2007)

u Outlook u A simple model for transport u Salen on Cu u SP-STM for molecules u Ab initio transport theory

LL RR  LL RR V  0

LL RR  V LL RR V ≠ 0 In equilibrium Out of equilibrium 2

LL RR  V LL RR V ≠ 0 2|E F -  |

 - 00 fNU  LL RR  V LL RR V ≠ 0 L LR R

E +eV/2 F E -eV/2 F T(E) E

I

H1H1 H0H0 H0H0 H1H1 H M (n) H0H0 H RM H0H0 H1H1 H0H0 H1H1 H0H0 H LM  R  L H= H M +H 0 +H 0 +H 0 +…. H M +  L (E)+  R (E)

Lead’s Self-energy Density Matrix Current Molecule Green function A. R. Rocha and S. Sanvito, PRB 70, (2004)

D. Sánchez-Portal, P. Ordejón, E. Artacho, and J.M. Soler, Int. J. Quant. Chem. 65, 453 (1997) KS-DFT Hamiltonian We implemented NEGF in Siesta  Localized multiple-z Pseudo-atomic orbitals (non-orthogonal)  Optimized Pseudopotential  Super-cells with up to 2,000 atoms

A. R. Rocha et al., Phys. Rev. B 73, (2006); Nature Materials 4, 335 (2005) Mailing list

Molecular Spin valves Nature Mat. 4, 335 (2005) Fe/MgO TMR junction I. Rungger et al DNA transport A.R.Rocha et al., in preparation Ni point contacts A.R.Rocha et al., cond-mat/ Problems with molecular transport C. Toher et al., PRL 95, (2005) Spin Torque M. Stamenova et al., in preparation

0nA 40nA 80nA 0nA 50nA 100nA Au on Au V=250mV d=0.4nm Ni on Ni V=250mV d=0.4nm

0% 10% 20% 500 mV250 mV -30% -10% 10% -70% -55% -40% -250 mV -60% -45% -30% -500 mV P=P= II I +I   I to tip I from tip

Does the GMR mirror the polarization ? -30% -10% 10% P=P= II I +I   -20% -15% -10% R=R= I P I AP I 250 mV

500 mV 250 mV -250 mV -500 mV 20% 10% -45% -50%

V=0

TIP M+S

    S S tip V

V=0 TIP M+S

V=400mV TIP M+S Current to the tip

V=0 TIP M+S

V=-400mV Current to the S+M TIP M+S

 Direct calculations of the tunneling currents are possible and include:  Some prospects of investigating the bonding of molecules on magnetic surfaces Electronic Structure of the tip Tip to sample interaction Charging of the moleculae Accurate determination of the spin-polarization Non-collinear spin Spin-orbit

Molecule N,N'-BIS(SALICYLIDENE)ETHYLENEDIAMINO-TM Where TM could be : Cu, Zn, Ni or Co C1 C2 C3 C1 C2 C3

Comparison between the DOS of the Salen molecule and the hypothetical small molecule E (eV) DOS (arb. units) Big Small

E (eV) Big Small

Molecule on Cu surfaces (un-relaxed) Cu-salen on Cu(001) Cu-salen on Cu(111) DOS (arb. units) E (eV)

Relaxation on Cu(001) surface Unrelaxed structure Relaxed structure

DOS for different TM-salen Cu E (eV) DOS (arb. units) 4s 1 3d 10

E (eV) DOS (arb. units) Zn 4s 2 3d 10

E (eV) DOS (arb. units) Co 4s 2 3d 7

E (eV) DOS (arb. units) Ni 4s 2 3d 8

Simulation STM images Free Cu-Salen E F -0.2eV < E < E F E F < E < E F +0.2eV I molecule to tip I tip to molecule

Constant current STM images Cu-Salen un-relaxed E F -0.2eV < E < E F E F < E < E F +0.2eV I molecule to tip I tip to molecule

(a)(b) (c)(d) E F -0.2eV < E < E F E F < E < E F +0.2eV I molecule to tip I tip to molecule Cu Zn

 This is very much work in progress First find the right atomic configuration Then simulate the current Compare the images for different TM Hopefully they will compare with experiments

integral of the DOS near Ef (pos. & neg. bias L-resolved DOS for Cu atom in the small molecule L-resolved DOS for Zn atom in the small molecule Cu DOS in free mole. and in mole. on Cu (001)